The methodology core (MC) will be directed by Dr. E. Francis Cook, professor of epidemiology at the Harvard School of Public Health, and will include a multidisciplinary group of collaborative investigators. The main role of the MC members will be to provide supervision and support for the design and analyses of the proposed projects. A critical objective of the MC will be to evaluate and develop the intervention strategies that have been proposed. Common analytic strategies will be promoted to maximize comparability of methodology and data quality between projects. An objective of the core will be to oversee the flow of data collected by these projects. This includes providing coordination and support for the development of all data collection instruments, subject recruitment, and training of interviewers and chart abstracters. For example, quality of data collection promoted by small pilot studies measuring inter- and intra-rater reliability of data collectors will be performed. In addition, the core members will identify and employ an appropriate data management system to enter, store, and retrieve all data. Quality control measures will be implemented to maintain accuracy and security of all data. The MC is comprised of members covering expertise in epidemiology, biostatistics, and health services research. A substantial degree of collaboration exists between members. These factors will be critical in maintaining optimal methodological supervision and development.